Eliminate potential distractions in advance
Some distractions you can prevent. Check the room in which you are going to speak and if there are any objects that may be in some way distracting, remove them if possible. If you can choose your own venue, aim for as quiet a location as you can find. This is the advice of famous coach Brian Tracy on his blog.
Other distractions may be completely beyond your control (e.g. a baby in the room starts crying or someone may be coughing loudly). What to do? Be prepared for them. Aim to stay on task and focus, regardless of any distractions you might reasonably expect. Accept that these things could happen: you will thus be better prepared if they do actually occur and have a better chance of ignoring the distraction and continuing with your presentation.
Be charming
You can act as a professional speaker by elegantly embracing and incorporating the distractions into your presentation. Sometimes a distraction will cause problems not only to you but also to the audience. In that case, you shouldn’t ignore it; on the contrary, draw the attention of the audience to the distraction by referring to it in a humorous way. Apologise briefly for the inconvenience and then continue with your presentation.
Know how much time you have left
Keeping track of the time is an excellent way to stay focused during your speech. Check at various times where you should be in the process. If you have the structure of the speech fixed in your mind, you can use time as something that leads you through. You could also have your own clock somewhere nearby so you can see the time with just a quick glance.
-jk-